The present invention relates to liquid crystal display apparatuses which require a transition of liquid crystal molecules in a liquid crystal layer from an initial alignment to a predetermined displayable alignment in advance of displaying. More particularly, this invention relates to an improvement in methods of driving such apparatuses with the transition of the alignment of liquid crystal molecules.
Various kinds of liquid crystal display apparatuses have conventionally been proposed and practicalized. In recent years, liquid crystal televisions have been expected to spread.
Widely used twisted nematic mode liquid crystal display apparatuses which employ nematic liquid crystals have shortcomings such as a slow response and a narrow viewing angle.
In-plane switching mode liquid crystal display apparatuses having a wide viewing angle have shortcomings in response speed and aperture ratio. Ferroelectric liquid crystal mode liquid crystal display apparatuses (hereinafter referred to as xe2x80x9cFLC type liquid crystal display apparatusesxe2x80x9d) exhibit a quick response and have a wide viewing angle, but also have great shortcomings in shock resistance, temperature property and the like.
In contrast, optically compensated bend mode (or optically compensated birefringence mode) liquid crystal display apparatuses (hereinafter, referred to as xe2x80x9cOCB mode liquid crystal display apparatusesxe2x80x9d), which were proposed in Japanese Unexamined Patent Publications No. Hei 7-84254 or Shingaku Technical Reports (EDI98-144, on page 19, published by the Corporation of Electricity Communication Institute) exhibit a quick response and have a wide viewing angle. The apparatuses, therefore, will be expected to be applied to liquid crystal televisions and the like as transmission or reflection type liquid crystal display apparatuses hereafter.
FIG. 7a shows an example of OCB mode liquid crystal display apparatuses. A liquid crystal pane 12 includes an array substrate 3a with transparent pixel electrodes 4a provided thereon, a counter substrate 3b with transparent counter electrodes 4b provided thereon and a liquid crystal layer 7 sandwiched between the array substrate 3a and the counter substrate 3b. Liquid crystal alignment layers 6a and 6b of polyimide are formed on internal surfaces of the array substrate 3a and the counter substrate 3b, on which the pixel electrodes 4a and the counter electrodes 4b are provided, respectively. Both the liquid crystal alignment layers 6a and 6b had been treated with rubbing, and the substrates 3a and 3b are disposed so that the rubbing directions of the liquid crystal alignment layers 6a and 6b are parallel to each other The liquid crystal layer 7 is filled with a nematic liquid crystal material having a positive dielectric anisotropy.
When a voltage is not applied between the pixel electrode 4a and the counter electrode 4b, pretilt angles of liquid crystal molecules 7a on both of the array substrate 3a and the counter substrate 3b are approximately several to 10 degrees in reverse directions. As shown in FIG. 7a, the liquid crystal molecules 7a offers an alignment such as to be inclined symmetrically and outwardly on a plane or a spray alignment.
In a case of an OCB mode liquid crystal display apparatus, by applying a voltage pulse hereinafter, referred to as xe2x80x9ca voltage pulse for transitionxe2x80x9d) with a comparatively high voltage between the pixel electrode 4a and the counter electrode 4b in a short time when a main power is switched on, for example, the liquid crystal molecules 7a having a spray alignment as shown in FIG. 7a locally rise and a micro area of bend alignment or bend alignment including twisted alignment (hereinafter, referred to as xe2x80x9ca transition corexe2x80x9d) is generated as shown in FIG. 7b. The transition core is spread by repeatedly applying the voltage pulse for transition. The transition of the whole liquid crystal material in the liquid crystal layer 7 to bend alignment enables an OCB mode liquid crystal display apparatus to display. An OCB mode liquid crystal display apparatus can display by utilizing a change in retardation resulting from a change in bend alignment of the liquid crystal molecule 7a, which is caused by applying display signal driving voltage.
On the external surface of the liquid crystal panel 2, there is disposed a phase-compensation plate 8 for optically compensating in order to enable a low voltage driving of the liquid crystal panel 2 as well as widen a viewing angle, with an optical axis thereof being fixed in a predetermined direction.
In a case of an OCB mode liquid crystal display apparatus, an inducement of such initially transition from spray alignment to bend alignment and a completion of the transition in the whole pixel area of the liquid crystal panel 2 in a short time are required before turning into an ordinary display-driving mode, as described above.
An FLC type liquid crystal display apparatus and a phase transition type liquid crystal display apparatus involve similar requirements before being shifted to an ordinary display-driving mode.
These liquid crystal display apparatuses have the following problems.
If the transition of the liquid crystal molecules to a displayable alignment is not carried out sufficiently, a fine display can not obtained when shifted to a display-driving mode. For example, in an OCB mode liquid crystal display apparatus, when the transition to bend alignment is not completed and an area of spray alignment remains locally, the remaining area becomes a bright point in display driving and looks like a point defect. The image is displayed dimly and unstably for several seconds to several minutes after starting display driving. Consequently, the transition to bend alignment must be certainly completed before being shifted to the display-driving mode. The transition core, however, is accidentally generated or not generated in the same place even if the voltage pulse for transition is applied on the same conditions, leading to the difficulty in certainly completing the transition in a short time.
Generally, a backlight is turned on when a main power of the apparatus is switched on. In liquid crystal televisions, an output of voice from a speaker starts simultaneously. However, in liquid crystal display apparatuses for carrying out the transition of the alignment of liquid crystal molecules in the liquid crystal layer to a predetermined alignment in advance of displaying, it occasionally takes a long time to be shifted to the ordinary display- driving mode. It is a waste of energy to switch on the backlight for the shift period to the display-driving mode or the transition period The display having many point alignment defects and plane alignment defects due to pixels with no transition or under transition as well as the blinking of the whole screen due to the application of the voltage pulse for transition are the causes of users"" discomfort and anxiety. Disappearance of the above-mentioned defects due to alignment transition can delete such sense of incongruity thereby realizing liquid crystal display apparatuses which can display images with high quality and are excellent in commercial view.
Operations of liquid crystal display apparatuses must be assured in a wide temperature range for being applied to various uses Further, in an OCB mode liquid crystal display apparatus, the transition to bend alignment must be certainly completed in a short time in such wide temperature range for assuring the operations.
In a 10-inch model active matrix type liquid crystal display apparatus, for example, the transition can be completed in a short time of 0.5 to 1 second at room temperatures of around 25xc2x0 C., while it occasionally takes along time, several minutes depending on conditions, for the whole liquid crystal layer to carry the transition to bend alignment at a low temperature in a range of xe2x88x9210 to 0xc2x0 C. That is, the OCB mode liquid crystal display apparatus is required to certainly complete the transition for displaying in a short time, several seconds at the longest in a wide temperature range as in a case of a general display apparatus.
The object of the present invention is to solve the above-mentioned problems thereby to provide methods of driving liquid crystal display apparatuses of which an initial alignment of liquid crystal molecules is different from the displayable alignment such as an OCB mode liquid crystal display apparatus, enabling a certainly completion of a transition of the liquid crystal molecules to the displayable alignment in a short time.
A method for driving a liquid crystal display apparatus in the present invention is a method for driving a liquid crystal display apparatus having a liquid crystal panel including a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, and a voltage-application unit for applying a voltage to the liquid crystal layer, in which an initial alignment of a liquid crystal material in the liquid crystal layer is different from a displayable alignment. In this method, the voltage for performing a transition of a liquid crystal material in a display area of the liquid crystal layer from the initial alignment to the displayable alignment is applied to the liquid crystal layer, in advance of displaying the liquid crystal panel, until the transition being carried out.
Preferably, a completion of the transition is determined after a product of a growth rate of an area of the liquid crystal layer being carried out the transition to the displayable alignment by a time for applying the voltage becomes more than an area of a display area of the liquid crystal panel. For example, the completion of the transition is determined when a product of a growth rate of an area of the liquid crystal layer being carried out the transition to the displayable alignment by a time for applying the voltage becomes larger than a predetermined value in a range of an area of a display area to twice the area of that.
Since a progression rate of the transition varies with a temperature, a time for applying the voltage for the transition is preferably set on the basis of a temperature of the liquid crystal panel measured in advance of applying the voltage for the transition, leading to the prevention of excess or insufficiency in applying voltage. If the voltage is applied to the liquid crystal layer for a time required for carrying out the transition of the liquid crystal layer in the display area to the displayable alignment at a predetermined lowest temperature in an operable temperature range, the transition is certainly completed in the whole operable temperature range.
In order to performing the transition of the liquid crystal layer in a display area, for example, after making a micro area of the liquid crystal layer being carried out the transition to the displayable alignment generates at each pixel or each area including a predetermined number of pixels, then the micro area is spread.
The micro area can be generated at a projection formed on a surface of the voltage-application unit or around a specific area on a liquid crystal alignment layer such that a pretilt angle of a liquid crystal material thereon is different from that of a liquid crystal material on another area.
In the case of forming the micro area at each pixel, a completion of the transition can be determined after a product of a growth rate of the micro area by a time for applying the voltage for the transition becomes larger than an area of the pixel. In the case of forming the micro per plural pixels, the completion of the transition can be determined similarly by comparing a product of a growth rate of the micro area by a time for applying the voltage with an area of pixels corresponding to the micro area.
The voltage for the transition is intermittently or continuously applied to the liquid crystal layer.
In the case of a transmission-type liquid crystal display apparatus including a backlight, it is preferable that the backlight is switched on after the completion of the application of the voltage to the liquid crystal layer.
This method for driving this liquid crystal display apparatus is useful for an OCB mode liquid crystal display apparatus in which the displayable alignment is a bend alignment, and the liquid crystal layer is carried out a transition from a spray alignment to the bend alignment in advance of displaying.
A liquid crystal display apparatus in the present invention has a liquid crystal panel with a plurality of pixels, the liquid crystal panel including: a pair of substrates with a rubbing-treated liquid crystal alignment formed thereon which are disposed so that the liquid crystal alignment layers face to each other and rubbing directions thereof are the same; a liquid crystal layer sandwiched between the pair of substrates; and a voltage-application unit for applying a voltage to the liquid crystal layer, wherein a length of the pixel in the rubbing direction is longer than a length of the pixel in a vertical direction to the rubbing direction.
The growth rate of the micro area in a rubbing direction is faster than that in a vertical direction to the rubbing direction. Accordingly, the parallelyzation of a longitudinal direction of the substrate with the rubbing direction can greatly shorten the time for transforming. A length of the pixel in the rubbing direction is longer than that of the pixel in a vertical direction to the rubbing direction, similarly leading to greatly shortening the time for transforming.
Another method for driving a liquid crystal display apparatus in the present invention is a method for driving a liquid crystal display apparatus having: a liquid crystal panel including a pair of substrates, a liquid crystal layer sandwiched between the pair of substrates, and a voltage-application unit for applying a voltage to the liquid crystal layer; and a backlight for projecting lights to the liquid crystal panel to display the liquid crystal panel, wherein an initial alignment of the liquid crystal layer is different from a displayable alignment. The method including a step of performing a transition of the liquid crystal layer to the displayable alignment by applying a voltage to the liquid crystal layer, and another step of switching on the backlight after a completion of applying the voltage for the transition of the liquid crystal layer.
In the case of a liquid crystal television, it is preferable that an application of the voltage to the liquid crystal layer and an output of a voice for broadcasting are started when a main power is switched on, and a display of images starts after completing the transition.
For example, the backlight is switched on only during an ordinary display-driving or displaying images.
This method for driving is particularly useful for an OCB mode liquid crystal display apparatus in which the liquid crystal layer is carried out a transition from a spray alignment as the initial alignment to a bend alignment as the displayable alignment in advance of displaying the liquid crystal panel.
This method for driving is used for a liquid crystal display apparatus having an active matrix type liquid crystal panel which includes a switching element at each pixel.
It is preferable that a completion of the transition is detailed so that an application of the voltage is finished and the backlight is switched on when a predetermined time passes after stating to apply the voltage for the transition of the liquid crystal layer.
In order to performing the transition of the liquid crystal layer to a predetermined displayable alignment in a short time, it is preferable to apply a higher voltage than a voltage of a voltage signal for displaying the liquid crystal panel. The transition, however, can also be progressed by applying a voltage equal to a voltage of a voltage signal for displaying. That is, a power supply system does not have to be prepared for each of transition-driving and display-driving, but an output voltage signal from a power supply system for display-driving can also be employed for a voltage signal for transforming.
In liquid crystal display apparatuses having a cover of the liquid crystal panel to be opened for use, such as a notebook type personal computer, a mobile computer and a folding portable phone, it is preferable to detect a progressional state of the transition in advance of switching on the backlight, being synchronized with an opening of the cover. That is, when the cover is opened, a judgement is done on whether the transition has been completed. If the transition has been completed, then the backlight is switched on, meanwhile. If not, the backlight is switched on after carrying out the transition.
An application of the voltage for the transition of the liquid crystal layer may be started, being synchronized with an opening of the cover.
It is preferable that the backlight is switched off, being synchronized with a dosing of the cover, so that a voltage is applied to the liquid crystal layer for maintaining the displayable alignment of the liquid crystal layer. It is also preferable that the backlight is switched on, being synchronized with an opening of the cover, so that the application of the voltage is finished.
It is also preferable to switch off the backlight so that a voltage is applied to the liquid crystal layer for maintaining the displayable alignment of the liquid crystal layer when an input signal from a user is not recognized for a predetermined time during a display driving. In such case, the application of the voltage is finished so that the backlight is switched on when an input signal from the user is recognized during the application of the voltage.
Preferably a progressional state or a completion of the transition of the liquid crystal material is notified to a user.
For example, it is notified to a user by a sound signal such as a voice from a speaker and by an optical signal or a display from a lamp, a light-emitting diode and an electroluminescence element. In the case of a liquid crystal television, it is preferable that an application of the voltage to the liquid crystal layer and an output of a voice for broadcasting by a speaker are started when a main power is switched on; and a voice signal for notifying a progressional state of the transition is superposed on a voice signal for broadcasting.
Another liquid crystal display apparatus in the present invention has a liquid crystal panel including: a liquid crystal layer of which initial alignment is different from a displayable alignment, a pair of substrates sandwiching the liquid crystal layer therebetween, and a voltage-application unit to the liquid crystal layer; a backlight for projecting lights to the liquid crystal panel to display the liquid crystal panel; a transition-driving unit for driving the voltage-application unit to apply a voltage to the liquid crystal layer thereby to performing a transition of the liquid crystal layer to the displayable alignment and for determining a completion of the transition of the liquid crystal layer; and a backlight-driving unit for switching on the backlight after the completion of the transition.
This liquid crystal display apparatus is useful for an OCB mode liquid crystal display apparatus in which the displayable alignment is a bend alignment; and the liquid crystal layer is carried out a transition from a spray alignment to the bend alignment in advance of displaying. Further, this liquid crystal display apparatus is also useful for a liquid crystal display apparatus having an active matrix type liquid crystal panel including a switching element at each pixel.
Preferably, a liquid crystal display apparatus further includes a switch for forcedly starting to apply a voltage by the voltage-application unit to performing a transition of the liquid crystal layer. When display defect resulting from transition defect is recognized in the liquid crystal panel, the transition is made on the liquid crystal layer again by the switch, leading to no display defect.
A further method for driving a liquid crystal display apparatus in the present invention is a method especially useful for driving an OCB mode liquid crystal display apparatus which has a liquid crystal panel including a pair of substrates, a liquid crystal layer held between the substrates, and a voltage-application unit to the liquid crystal layer, and the method including, in advance of displaying images, a step of measuring a temperature of the liquid crystal panel; another step of determining a condition of a voltage pulse for performing the transition of the liquid crystal layer to a bend alignment on the basis of the measured temperature; and a further step of applying the voltage pulse to the liquid crystal layer according to the determined condition.
In a preferred mode of the present invention, a frequency of the voltage pulse is determined on the basis of the measured temperature in the step of determining a condition of the voltage pulse. In such case, preferably, a frequency of the voltage pulse is set to be higher at a high temperature than at a low temperature. For example, a frequency of the voltage pulse is set to be 2 to 5 Hz at the temperature of 20xc2x0 C. or more; and a frequency of the voltage pulse is set to be 0.2 to 1 Hz at the temperature of 0xc2x0 C. or less. More preferably, a frequency of the voltage pulse is set to be in a range of 2.5 to 4 Hz at the temperature of 20xc2x0 C. or more; and a frequency of the voltage pulse is set to be in a range of 0.4 to 0.6 Hz at the temperature of 0xc2x0 C. or less.
In another preferred mode of the present invention, a voltage value of the voltage pulse is determined on the basis of the measured temperature in the step of determining a condition of the voltage pulse. In this case, preferably, a voltage value of the voltage pulse is set to be higher at a low temperature than at a high temperature.
In a further preferred mode of the present invention, a frequency and a voltage value of the voltage pulse are determined on the basis of the measured temperature in the step of determining a condition of the voltage pulse.
In a still further preferred mode of the present invention, a pulsewidth of the voltage pulse is determined on the basis of the measured temperature in the step of determining a condition of the voltage pulse.
A condition of the voltage pulse varies continuously in accordance with a temperature of the liquid crystal panel.
The condition of the voltage pulse may vary gradually. For example, the condition of the voltage pulse to be determined is set for each predetermined divided temperature range in the step of determining the condition of the voltage pulse. An operable temperature range is divided into the two temperature ranges such as high temperature and low temperature, for example.
If an initial period such that a voltage applied to the liquid crystal layer is approximately 0 V is set immediately before applying the voltage pulse in the step of applying the voltage pulse, the transition can be completed in a short time. The initial period is set to be, preferably, 0.2 to 5 seconds. In the case of intermittently applying a plurality of the voltage pulses, it is effective to set a period such that an electric potential between the pair of electrodes as the voltage-application unit is approximately 0 V in an interval between the voltage pulses.
The voltage pulse is simultaneously applied at all pixels, resulting in the completion of the transition in a short time.
In the case of a transmission type liquid crystal display apparatus having a backlight, it is preferable that the backlight is switched on after the transition of the liquid crystal layer to a bend alignment by applying the voltage pulse.
This method is used for an active matrix type liquid crystal display apparatus comprising a switching element at each pixel for example.
A still further method for driving a liquid crystal display apparatus in the present invention is a method especially useful for driving an OCB mode liquid crystal display apparatus, and, in advance of displaying an image, the voltage pulse is applied to the liquid crystal layer, in the whole operable temperature range, according to a condition of a voltage pulse to be applied to the liquid crystal layer for carrying out the transition of the liquid crystal layer to a bend alignment in a short time at a lowest operable temperature. That is, the voltage pulse is applied to the liquid crystal layer in the whole operable temperature range according to a condition of a voltage pulse at a temperature at which the voltage pulse should be applied for a longer time. Thus, the transition can be completed in a comparatively short time at any operable temperature. For example, it is preferable to apply the voltage pulse having a frequency selected from a range of 0.2 to 1 Hz more preferably, 0.4 to 0.6 Hz.
A further liquid crystal display apparatus in the present invention has a liquid crystal panel including a pair of substrates, a liquid crystal layer held between the substrates, and a voltage-application unit for applying a voltage to the liquid crystal layer; a temperature-detecting unit for detecting a temperature of the liquid crystal panel; and a condition-determining unit for determining a condition of a voltage pulse to be applied by the voltage-application unit for performing the transition of the liquid crystal layer to a bend alignment on the basis of a temperature of the liquid crystal panel detected by the means of detecting a temperature of the liquid crystal panel.
The present invention is especially usefull for so called OCB mode liquid crystal display apparatus.
In the present invention, the phrase xe2x80x9cturning on the backlightxe2x80x9d means making the backlight emit light for displaying images. On the other hand, the phrase xe2x80x9cturning off the backlightxe2x80x9d includes reducing an intensity of the light so as to disable the backlight for displaying images even when the backlight maintains an electrical connection besides a general OFF state.